U.S. patent number 9,508,858 [Application Number 14/872,673] was granted by the patent office on 2016-11-29 for contacts for highly scaled transistors.
This patent grant is currently assigned to TAIWAN SEMICONDUCTOR MANUFACTURING COMPANY, LTD.. The grantee listed for this patent is Taiwan Semiconductor Manufacturing Company, Ltd.. Invention is credited to Chia-Hao Chang, Jean-Pierre Colinge, Carlos H. Diaz, Ying-Keung Leung, Wai-Yi Lien, Chun-Hsiung Lin, Chih-Hao Wang, Chung-Cheng Wu.
United States Patent |
9,508,858 |
Diaz , et al. |
November 29, 2016 |
Contacts for highly scaled transistors
Abstract
A semiconductor device and methods of forming the same are
disclosed. The semiconductor device includes a substrate, first and
second source/drain (S/D) regions, a channel between the first and
second S/D regions, a gate engaging the channel, and a contact
feature connecting to the first S/D region. The contact feature
includes first and second contact layers. The first contact layer
has a conformal cross-sectional profile and is in contact with the
first S/D region on at least two sides thereof. In embodiments, the
first contact layer is in direct contact with three or four sides
of the first S/D region so as to increase the contact area. The
first contact layer includes one of a semiconductor-metal alloy, an
III-V semiconductor, and germanium.
Inventors: |
Diaz; Carlos H. (Mountain View,
CA), Wu; Chung-Cheng (Hsin-Chu County, TW), Chang;
Chia-Hao (Hsinchu, TW), Wang; Chih-Hao (Hsinchu
County, TW), Colinge; Jean-Pierre (Hsinchu,
TW), Lin; Chun-Hsiung (Hsinchu County, TW),
Lien; Wai-Yi (Hsinchu, TW), Leung; Ying-Keung
(Hong Kong, HK) |
Applicant: |
Name |
City |
State |
Country |
Type |
Taiwan Semiconductor Manufacturing Company, Ltd. |
Hsin-Chu |
N/A |
TW |
|
|
Assignee: |
TAIWAN SEMICONDUCTOR MANUFACTURING
COMPANY, LTD. (Hsin-Chu, TW)
|
Family
ID: |
55855559 |
Appl.
No.: |
14/872,673 |
Filed: |
October 1, 2015 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20160141423 A1 |
May 19, 2016 |
|
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
62081348 |
Nov 18, 2014 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L
23/53271 (20130101); H01L 23/5283 (20130101); H01L
29/78696 (20130101); H01L 29/78618 (20130101); H01L
29/78642 (20130101); H01L 29/45 (20130101); H01L
29/42392 (20130101); H01L 29/775 (20130101); H01L
29/41791 (20130101); H01L 29/785 (20130101); H01L
23/5226 (20130101); H01L 29/66666 (20130101); H01L
29/41733 (20130101); H01L 29/41741 (20130101); H01L
21/76852 (20130101); H01L 2029/7858 (20130101); H01L
29/7827 (20130101); H01L 29/7853 (20130101) |
Current International
Class: |
H01L
21/336 (20060101); H01L 29/45 (20060101); H01L
29/66 (20060101); H01L 29/423 (20060101); H01L
29/417 (20060101); H01L 29/786 (20060101) |
Field of
Search: |
;438/283-284 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Saraswat, Krishna et al., "High Mobility MOSFETs," Department of
Electrical Engineering, Stanford University, INMP May 14, 2014, 15
pages. cited by applicant.
|
Primary Examiner: Doan; Theresa T
Attorney, Agent or Firm: Haynes and Boone, LLP
Parent Case Text
This claims the benefit of U.S. Prov. No. 62/081,348 entitled
"Contacts for Highly Scaled Transistors," filed Nov. 18, 2014,
herein incorporated by reference in its entirety.
Claims
What is claimed is:
1. A method of forming a contact in a vertical gate-all-around
(VGAA) device, comprising: receiving a VGAA device, the VGAA device
having: a substrate; a first source/drain (S/D) region over the
substrate; an isolation structure over the substrate and
surrounding the first S/D region; a channel over the first S/D
region; a second S/D region over the channel; a gate wrapping
around the channel; and a dielectric layer over the isolation
structure and the first S/D region; etching the dielectric layer
and the isolation structure to form an opening, wherein the opening
exposes at least two sides of the first S/D region; forming a first
contact layer in the opening, wherein the first contact layer has a
conformal cross-sectional profile and is in contact with the first
S/D region; and forming a second contact layer in the opening over
the first contact layer.
2. The method of claim 1, wherein the first contact layer includes
one of InAs, InGaAs, InP, and Ge.
3. The method of claim 1, wherein the first contact layer includes
a semiconductor-metal alloy.
4. The method of claim 1, wherein the opening exposes a top surface
and two sidewall surfaces of the first S/D region.
5. A method of forming a contact in a multi-gate semiconductor
device, comprising: receiving a multi-gate semiconductor device
having: a substrate; first and second source/drain (S/D) regions; a
channel between the first and second S/D regions; a gate engaging
the channel; and a dielectric layer over the first S/D region;
etching the dielectric layer to form an opening, wherein the
opening exposes at least two sides of the first S/D region; forming
a first contact layer in the opening, wherein the first contact
layer has a conformal cross-sectional profile and is in contact
with the first S/D region; and forming a second contact layer in
the opening over the first contact layer.
6. The method of claim 5, wherein the first contact layer includes
one of III-V semiconductors.
7. The method of claim 5, wherein: the first contact layer includes
a material selected from the group consisting of titanium, cobalt,
nickel, nickel cobalt, and germanium.
8. The method of claim 5, wherein the multi-gate semiconductor
device further includes a contact etch stop (CES) layer between the
dielectric layer and the first S/D region, wherein the etching of
the dielectric layer includes: etching the CES layer within the
opening to expose the at least two sides of the first S/D
region.
9. The method of claim 5, wherein the first S/D region is a fin
structure having opposing sidewall surfaces.
10. The method of claim 9, wherein forming the first contact layer
in the opening includes forming the first contact layer directly on
the opposing sidewall surfaces such that the first contact layer
physically contacts the opposing sidewall surfaces.
11. The method of claim 5, further comprising: epitaxially growing
a semiconductor material on the first S/D region to form a diamond
shaped S/D feature, the diamond shaped S/D feature having a first
side, a second side, a third side, and a fourth side, and wherein
forming the first contact layer in the opening includes forming the
first contact layer directly on the first side, the second side,
the third side, and the fourth side.
12. The method of claim 5, further comprising: forming a
semiconductor material on the first S/D region to form a
multi-sided S/D feature, the multi-sided S/D feature having a first
side surface and a second side surface, wherein forming the first
contact layer in the opening includes forming the first contact
layer directly on the first side surface without forming the first
contact layer directly on the second side surface.
13. A method comprising: forming a gate stack over a substrate;
forming a source/drain feature over the substrate, the source/drain
feature having a first side surface, a second side surface, and a
third side surface; forming a dielectric layer over the
source/drain feature and the gate stack; forming a trench through
the dielectric layer to expose at least the first side surface, the
second side surface, and third side surface; forming a first
contact layer in the trench such that the first contact layer
physically contacts the first side surface, the second side
surface, and third side surface; and forming a second contact layer
in the trench over the first contact layer.
14. The method of claim 13, wherein after forming the first contact
layer in the trench, at least one of the first side surface, the
second side surface, and the third side surface includes a portion
that physically contacts the dielectric layer.
15. The method of claim 13, wherein the first side surface
intersects the second side surface, and wherein the third side
surface intersects the second side surface without intersecting the
first side surface.
16. The method of claim 13, further comprising forming a fin
structure over the substrate, and wherein forming the source/drain
feature over the substrate includes forming the source/drain
feature directly on the fin structure.
17. The method of claim 16, wherein the first side surface and the
second side surface directly interface with the fin structure.
18. The method of claim 13, wherein the first contact layer
includes a III-V semiconductor material layer, and wherein the
second contact layer includes a metallic material layer.
19. The method of claim 13, further comprising forming another
source/drain feature over the substrate, and wherein forming the
trench through the dielectric layer further exposes the another
source/drain feature, and wherein forming the first contact layer
in the trench further includes forming the first contact layer
directly on the another source/drain feature such that the first
contact layer physically contacts the another source/drain feature,
the first contact layer extending continuously from the
source/drain feature to the another source/drain feature.
20. The method of claim 19, wherein the source/drain feature
physically contacts the another source/drain feature.
Description
BACKGROUND
The semiconductor integrated circuit (IC) industry has experienced
exponential growth. Technological advances in IC materials and
design have produced generations of ICs where each generation has
smaller and more complex circuits than the previous generation. In
the course of IC evolution, functional density (i.e., the number of
interconnected devices per chip area) has generally increased while
geometry size (i.e., the smallest component (or line) that can be
created using a fabrication process) has decreased. This scaling
down process generally provides benefits by increasing production
efficiency and lowering associated costs. Such scaling down has
also increased the complexity of processing and manufacturing
ICs.
For example, multi-gate field effect transistors (FET) have been
developed for their high drive currents, small footprints, and
excellent control of short-channel effects. Examples of multi-gate
FET include the double-gate FET, the triple-gate FET, the
omega-gate FET, and the gate-all-around (or surround-gate) FET
including both the horizontal gate-all-around (HGAA) FET and the
vertical gate-all-around (VGAA) FET. The multi-gate FETs are
expected to scale the semiconductor process technology beyond the
limitations of the conventional bulk metal-oxide-semiconductor FET
(MOSFET) technology. However, as the transistor device structure
scales down and becomes three dimensional, the transistor contact
resistance exhibits increased impact on the device performance.
With conventional contact formation scheme, transistor contact
resistance in highly scaled multi-gate FETs may limit the devices'
intrinsic performance well over 50%.
BRIEF DESCRIPTION OF THE DRAWINGS
The present disclosure is best understood from the following
detailed description when read with the accompanying figures. It is
emphasized that, in accordance with the standard practice in the
industry, various features are not drawn to scale and are used for
illustration purposes only. In fact, the dimensions of the various
features may be arbitrarily increased or reduced for clarity of
discussion.
FIG. 1 shows a flow chart of a method of fabricating a
semiconductor device, according to various aspects of the present
disclosure.
FIGS. 2A, 2B, 2C, 3A, 3B, 4A, 4B, 5A, and 5B are perspective and
cross-sectional views of forming a semiconductor device according
to the method of FIG. 1, in accordance with some embodiments.
FIGS. 6A, 6B, 7A, 7B, 8A, 8B, 9A, and 9B are cross-sectional views
of forming a semiconductor device according to the method of FIG.
1, in accordance with some embodiments.
FIGS. 10A and 10B are cross-sectional views of a semiconductor
device constructed in accordance with some embodiments of the
method of FIG. 1.
FIGS. 10C, 10D, 10E, 10F, 10G, 10H, 10I, 10J, 10K, 10L, 10M, 10N,
10O, and 10P are cross-sectional views of semiconductor devices
constructed in accordance with some embodiments of the method of
FIG. 1.
FIGS. 11A and 11B are cross-sectional views of another
semiconductor device constructed in accordance with some
embodiments of the method of FIG. 1.
FIG. 12 shows a flow chart of a method of fabricating a
semiconductor device, according to various aspects of the present
disclosure.
FIGS. 13A, 13B, 14A, 14B, 15, 16, 17, 18, and 19 are perspective
and cross-sectional views of forming a semiconductor device
according to the method of FIG. 2, in accordance with some
embodiments.
FIG. 20 is a cross-sectional view of another semiconductor device
formed with an embodiment of the method of FIG. 2.
FIGS. 21, 22, 23, 24, and 25 are cross-sectional views of forming
the semiconductor device of FIG. 20, in accordance with some
embodiments.
DETAILED DESCRIPTION
The following disclosure provides many different embodiments, or
examples, for implementing different features of the provided
subject matter. Specific examples of components and arrangements
are described below to simplify the present disclosure. These are,
of course, merely examples and are not intended to be limiting. For
example, the formation of a first feature over or on a second
feature in the description that follows may include embodiments in
which the first and second features are formed in direct contact,
and may also include embodiments in which additional features may
be formed between the first and second features, such that the
first and second features may not be in direct contact. In
addition, the present disclosure may repeat reference numerals
and/or letters in the various examples. This repetition is for the
purpose of simplicity and clarity and does not in itself dictate a
relationship between the various embodiments and/or configurations
discussed.
Further, spatially relative terms, such as "beneath," "below,"
"lower," "above," "upper" and the like, may be used herein for ease
of description to describe one element or feature's relationship to
another element(s) or feature(s) as illustrated in the figures. The
spatially relative terms are intended to encompass different
orientations of the device in use or operation in addition to the
orientation depicted in the figures. The apparatus may be otherwise
oriented (rotated 90 degrees or at other orientations) and the
spatially relative descriptors used herein may likewise be
interpreted accordingly.
The present disclosure is generally related to semiconductor
devices, and more particularly to semiconductor devices having
multi-gate transistors such as horizontal multi-gate transistors
and vertical multi-gate transistors. Examples of horizontal
multi-gate transistors include the double-gate FET, the triple-gate
FET, the omega-gate FET, and the horizontal gate-all-around (HGAA)
FET. Examples of vertical multi-gate transistors include the
vertical gate-all-around (VGAA) FET and tunneling FET (TFET).
Furthermore, the HGAA FET and VGAA FET may include one or more of
the nanowire channel, the bar-shaped channel, or other suitable
channel structures. An objective of the present disclosure is to
provide novel source/drain (S/D) contacts for the multi-gate
transistors, wherein the novel S/D contacts have reduced contact
resistance compared to the conventional S/D contacts.
In the following discussion, various embodiments of the present
disclosure are described in the context of fabricating devices 100,
200, 300, 400, 500, 600, and 700. These devices are non-limiting
examples that can be manufactured with some embodiments of the
present disclosure. Furthermore, each of the devices 100, 200, 300,
400, 500, 600, and 700 may be an intermediate device fabricated
during processing of an integrated circuit (IC), or a portion
thereof, that may comprise static random access memory (SRAM)
and/or other logic circuits, passive components such as resistors,
capacitors, and inductors, and active components such as p-type
FETs, n-type FETs, metal-oxide semiconductor field effect
transistors (MOSFET), complementary metal-oxide semiconductor
(CMOS) transistors, bipolar transistors, high voltage transistors,
high frequency transistors, other memory cells, and combinations
thereof.
First Embodiment
The first embodiment of the present disclosure is now described
with reference to FIGS. 1-5B in fabricating the device 100. FIG. 1
shows a flow chart of a method 10 of forming a semiconductor
device, such as a semiconductor device having a multi-gate
structure, according to various aspects of the present disclosure.
The method 10 is merely an example, and is not intended to limit
the present disclosure beyond what is explicitly recited in the
claims. Additional operations can be provided before, during, and
after the method 10, and some operations described can be replaced,
eliminated, or moved around for additional embodiments of the
method.
At operation 12, the method 10 (FIG. 1) receives the device 100 as
shown in FIGS. 2A, 2B and 2C, wherein FIG. 2A is a perspective
schematic view of the device 100, FIG. 2B is a cross-sectional view
of the device 100 along the "A-A" line of FIG. 2A, and FIG. 2C is a
cross-sectional view of the device 100 along the "B-B" line of FIG.
2A. Referring to FIGS. 2A, 2B, and 2C collectively, the device 100
includes a substrate 102, a fin 104, an isolation structure 106, a
gate 108, and a dielectric layer 110. The fin 104 projects upwardly
(along the "z" direction) from the substrate 102. The isolation
structure 106 is disposed over the substrate and adjacent to a
bottom portion of the fin 104. It isolates the fin 104 from other
active regions (not shown) of the device 100. The gate 108 is
formed over the isolation structure 106 and engages the fin 104 on
three sides thereof. Therefore, the device 100 as shown is a
triple-gate device. Other types of gate structures, such as
double-gate (e.g., the gate 108 engages two side surfaces of the
fin 104), omega-gate (e.g., the gate 108 fully engages a top
surface and two side surfaces of the fin 104 and partially engages
a bottom surface of the fin 104), and gate-all-around (e.g., the
gate 108 fully engages top, bottom, and two side surfaces of the
fin 104) are within the scope of the present disclosure. The
dielectric layer 110 is disposed over the fin 104, the isolation
structure 106, and the gate 108. The various elements of the device
100 will be further described in the following sections.
The substrate 102 is a silicon substrate in the present embodiment.
Alternatively, the substrate 102 may comprise another elementary
semiconductor, such as germanium; a compound semiconductor
including silicon carbide, gallium arsenic, gallium phosphide,
indium phosphide, indium arsenide, and/or indium antimonide; an
alloy semiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GaInAs,
GaInP, and/or GaInAsP; or combinations thereof.
The fin 104 is suitable for forming an n-type FET or a p-type FET.
The fin 104 may be fabricated using suitable processes including
photolithography and etch processes. The photolithography process
may include forming a photoresist layer (resist) overlying the
substrate 102, exposing the resist to a pattern, performing
post-exposure bake processes, and developing the resist to form a
masking element including the resist. The masking element is then
used for etching recesses into the substrate 102, leaving the fin
104 on the substrate 102. The etching process can include dry
etching, wet etching, reactive ion etching (RIE), and/or other
suitable processes. Alternatively, the fin 104 may be formed using
mandrel-spacer double patterning lithography. Numerous other
embodiments of methods to form the fin 104 may be suitable.
The isolation structure 106 may be formed of silicon oxide, silicon
nitride, silicon oxynitride, fluoride-doped silicate glass (FSG), a
low-k dielectric material, and/or other suitable insulating
material. The isolation structure 106 may be shallow trench
isolation (STI) features. In an embodiment, the isolation
structures 106 is formed by etching trenches in the substrate 102,
e.g., as part of the fin 104 formation process. The trenches may
then be filled with isolating material, followed by a chemical
mechanical planarization (CMP) process. Other isolation structure
such as field oxide, LOCal Oxidation of Silicon (LOCOS), and/or
other suitable structures are possible. The isolation structure 106
may include a multi-layer structure, for example, having one or
more thermal oxide liner layers.
The fin 104 and the gate 108 are further illustrated with reference
to FIG. 2B. Referring to FIG. 2B, the fin 104 includes two
source/drain (S/D) regions (or features) 104a and a channel region
104b between the two S/D regions 104a. The S/D regions 104a and the
channel region 104b are arranged in a horizontal manner (along the
"y" direction) over the isolation structure 106. Therefore, the
device 100 is a horizontal multi-gate device. The gate 108 includes
a gate stack 108a and a gate spacer 108b on sidewalls of the gate
stack 108a. The gate stack 108a engages the fin 104 at the channel
region 104b. In various embodiments, the gate stack 108a includes a
multi-layer structure. In one example, the gate stack 108a includes
an interfacial layer and a poly-silicon layer. In another example,
the gate stack 108a includes an interfacial layer, a high-k
dielectric layer, a barrier layer, a work function metal layer, and
a metal fill layer. Various other embodiments of the gate stack
108a are possible. The gate stack 108a may be formed using either a
"gate-first" or a "gate-last" method. In embodiments, the gate
spacer 108b includes a dielectric material, such as silicon nitride
or silicon oxynitride and is formed by one or more deposition and
etching processes.
The dielectric layer 110, also referred to as an inter-layer
dielectric (ILD) layer, is disposed over the various structures
discussed above. In embodiments, the device 100 further includes a
contact etch stop (CES) layer underneath the ILD layer 110. The ILD
layer 110 may include materials such as tetraethylorthosilicate
(TEOS) oxide, un-doped silicate glass, or doped silicon oxide such
as borophosphosilicate glass (BPSG), fused silica glass (FSG),
phosphosilicate glass (PSG), boron doped silicon glass (BSG),
and/or other suitable dielectric materials. The ILD layer 110 may
be deposited by a plasma-enhanced chemical vapor deposition (PECVD)
process or other suitable deposition technique. In an embodiment,
the ILD layer 110 is formed by a flowable CVD (FCVD) process. The
FCVD process includes depositing a flowable material (such as a
liquid compound) on the substrate 102 to fill trenches and
converting the flowable material to a solid material by a suitable
technique, such as annealing in one example. After various
deposition processes, a chemical mechanical planarization (CMP)
process is performed to planarize a top surface of the ILD layer
110.
At operation 14, the method 10 (FIG. 1) etches the ILD layer 110 to
form an opening (or a contact hole) 112. Referring to FIGS. 3A and
3B, FIG. 3A is a cross-sectional view of the device 100 along the
"A-A" line of the FIG. 2A after the operation 14, and FIG. 3B is a
cross-sectional view of the device 100 along the "B-B" line of the
FIG. 2A after the operation 14. The opening 112 has a bottom
surface 112' that is below a top surface 104a' of the fin 104a. The
portion of the fin 104 exposed in the opening 112 has a height "R"
which is also the vertical distance between the bottom surface 112'
and the top surface 104a' along the z direction. The portion of the
fin 104 above the isolation structure 106 has a height "F." In
embodiments, R is greater than half of F. In some embodiments, R
ranges from about 5 nanometer (nm) to about 60 nm. In an example,
the opening 112 may be etched into the isolation structure 106. The
opening 112 is deeper than conventional contact holes which
typically stop at the top surface 104a'. One benefit of having a
deep opening 112 is that an S/D contact formed therein will have
larger contact areas with the S/D region 104a.
In various embodiments, the opening 112 has a top width T and a
bottom width B along the x direction, and a height H along the z
direction. The bottom width B is greater than the width w.sub.f of
the fin 104a along the x direction. The top width T is greater than
the bottom width B. Accordingly, the sidewalls of the opening 112
are slanted. The dimensions T, B, and H should be designed such
that all surfaces of the opening 112 are easily accessible when a
conductive material is deposited into the opening 112 to form a
contact, as will be shown later. For the same consideration, the
distances, b.sub.1 and b.sub.2, from the sidewalls of the opening
112 to the sidewalls of the fin 104a are designed such that the
bottom and sidewalls of the opening 112 as well as the sidewalls of
the fin 104a are easily accessible during the deposition of the
conductive material. In various embodiments, T ranges from about 12
to about 40 nm, B ranges from about 8 to about 30 nm, and H ranges
from about 50 to about 150 nm. In various embodiments, b1 and b2
each ranges from about half (1/2) of w.sub.f to about one and half
(11/2) of w.sub.f. In addition, although FIG. 3B shows the opening
112 to be about symmetrical about the fin 104a in the z-x plane,
this is merely exemplary in nature and does not limit the present
disclosure. For example, in embodiments, b.sub.1 and b.sub.2 may be
different.
The etching processes may include a suitable wet etch, dry (plasma)
etch, and/or other processes. For example, a dry etching process
may use chlorine-containing gases, fluorine-containing gases, other
etching gases, or a combination thereof. The wet etching solutions
may include NH.sub.4OH, HF (hydrofluoric acid) or diluted HF,
deionized water, TMAH (tetramethylammonium hydroxide), other
suitable wet etching solutions, or combinations thereof.
In an embodiment, the device 100 includes a contact etch stop (CES)
layer underneath the ILD layer 110 but over the S/D regions 104 and
over the gate 108. For example, the CES layer may be made of a
material similar to that for the isolation structure 106, such as
silicon oxide or silicon nitride. During the operation 14, the CES
layer protects the fin 104 from over-etching. If a contact hole to
the gate 108 is etched at the same time, the CES layer further
protects the gate 108 from over-etching. To further this
embodiment, the operation 14 further includes an etching process
tuned to remove the CES layer within the opening 112, thereby
exposing the S/D regions 104a for contact formation.
In yet another embodiment, the device 100 includes a contact etch
stop (CES) layer over the S/D regions 104 and over the gate 108.
Prior to forming the ILD layer 110, the method 10 partially removes
the CES layer so that the S/D regions 104a are exposed to provide
top and sidewall surfaces for subsequent S/D contact formation. To
further this embodiment, once the operation 14 removes the ILD
layer 110 to form the opening 112, the fin surfaces for S/D contact
formation are exposed.
At operation 16, the method 10 (FIG. 1) forms a first contact layer
114 in the opening 112. Referring to FIGS. 4A and 4B, FIG. 4A is a
cross-sectional view of the device 100 along the "A-A" line of the
FIG. 2A after the operation 16, and FIG. 4B is a cross-sectional
view of the device 100 along the "B-B" line of the FIG. 2A after
the operation 16. The first contact layer 114 is formed over the
surfaces of the opening 112. In particular, it is formed over the
top surface and sidewalls of the S/D region 104a. The first contact
layer 114 has a conformal profile, i.e. it has a near uniform
thickness over the surfaces of the opening 112. In an embodiment,
the first contact layer 114 has a thickness ranging from about 2 nm
to about 10 nm. In an embodiment, the first contact layer 114
includes a semiconductor-metal alloy. For example, the
semiconductor-metal alloy may include a metal material such as
titanium, cobalt, nickel, nickel cobalt, other metals, or a
combination thereof. To further this embodiment, the metal material
is deposited using a chemical vapor deposition (CVD), physical
vapor deposition (PVD), atomic layer deposition (ALD), or other
suitable deposition techniques. Then, an annealing process is
performed thereby forming a semiconductor-metal alloy over the
surfaces of the S/D regions 104a. In another embodiment, the first
contact layer 114 includes one or more III-V semiconductors that
provide high carrier mobility and/or suitable band structure for
tuning energy barrier. For example, the first contact layer 114 may
include InAs, InGaAs, InP, or other suitable III-V semiconductors.
In yet another embodiment, the first contact layer 114 includes
germanium (Ge). In various embodiments, the first contact layer 114
may be deposited using CVD, PVD, ALD, or other suitable methods. In
various embodiments, the material of the first contact layer 114
offers low or negligible energy barrier for charge carriers flowing
into and out of the transistor channel. The first contact material
coupled with increased contact area reduces the contact resistance
to the S/D regions 104a.
At operation 18, the method 10 (FIG. 1) forms a second contact
layer 116 in the opening 112 over the first contact layer 114.
Referring to FIGS. 5A and 5B, FIG. 5A is a cross-sectional view of
the device 100 along the "A-A" line of the FIG. 2A after the
operation 18, and FIG. 5B is a cross-sectional view of the device
100 along the "B-B" line of the FIG. 2A after the operation 18. The
second contact layer 116 fills the remaining space of the opening
112. The second contact layer 116 may include one or more layers of
metallic materials, such as metallic nitrides, metallic or
conductive oxides, elemental metals, or combinations thereof. For
example, the second contact layer 116 may use tungsten (W), copper
(Cu), cobalt (Co), and/or other suitable materials. In various
embodiments, the second contact layer 116 may be formed by CVD,
PVD, plating, and/or other suitable processes. As shown in FIGS. 5A
and 5B, an S/D contact 118 is formed in each of the openings 112,
conductively connecting to the respective S/D regions 104a. The S/D
contact 118 includes the first contact layer 114 and the second
contact layer 116. Various dimensions of the S/D contact 118 are
labeled in FIG. 5B, including a top width "T," a bottom width "B,"
and a height "H." The relationship among T, B, H, and the width
w.sub.f of the fin 104a has been discussed with reference to FIG.
3B. In various embodiments, T ranges from about 12 to about 40 nm,
B ranges from about 8 to about 30 nm, and H ranges from about 50 to
about 150 nm.
At operation 20, the method 10 (FIG. 1) performs further steps to
complete the fabrication of the device 100. For example, the
operation 20 may form a gate contact electrically connecting the
gate stack 108a, and may form metal interconnects connecting the
multi-gate FET to other portions of the device 100 to form a
complete IC.
Second Embodiment
The second embodiment of the present disclosure is now described
with reference to FIGS. 1 and 6A-9B, wherein the device 200 is
fabricated according to some embodiments of the method 10. FIGS.
6A-9B illustrate cross-sectional views of the device 200 in the
process of fabrication. Discussions applicable to both the devices
100 and 200 are abbreviated or omitted below for the sake of
simplicity.
At the operation 12, the method 10 (FIG. 1) receives the device
200, which is similar to the device 100 (FIGS. 2A-2C) in many
respects. For the purpose of simplicity, same reference numerals
are used to label similar elements of the two devices. For example,
as shown in FIGS. 6A and 6B, the device 200 also includes a
substrate 102, a fin 104, an isolation structure 106, a gate 108,
and an ILD layer 110. The gate 108 also includes a gate stack 108a
and a gate spacer 108b. The gate stack 108a engages a channel
region 104b of the fin 104. One difference between the devices 100
and 200 lies in the structure of the S/D regions of the two
devices. As shown in FIG. 6B, the device 200 has diamond-shaped S/D
regions 204a. In an embodiment, the S/D regions 204a are formed by
etching a portion of the fin 104 of the device 200 to form recesses
therein and epitaxially growing one or more semiconductor features
from the recesses. For example, the etching process may use a dry
etching, a wet etching, or other suitable etching methods. A
cleaning process may be performed that cleans the recesses with a
hydrofluoric acid (HF) solution or other suitable solution.
Subsequently, one or more epitaxial growth processes are performed
to grow semiconductor (e.g., silicon) features in the recesses. The
epitaxial growth process may in-situ dope the grown semiconductor
with a p-type dopant for forming a p-type FET or an n-type dopant
for forming an n-type FET. As further illustrated in FIG. 6B, the
S/D regions 204a each have two upwardly facing surfaces (or sides)
204a' and two downwardly facing surfaces (or sides 204a'').
At the operation 14, the method 10 (FIG. 1) etches the ILD layer
110 of the device 200 to form an opening 112 therein. Referring to
FIGS. 7A and 7B, the opening 112 has a bottom surface 112' that is
below the surfaces 204a'. The portion of the fin 104/204a exposed
in the opening 112 has a height "R." The portion of the fin
104/204a above the isolation structure 106 has a height "F." In
embodiments, R is greater than half of F. In embodiments, the
opening 112 fully exposes the surface 204a' and may partially or
fully expose the surfaces 204a''. In some embodiments, R ranges
from about 5 nanometer (nm) to about 60 nm. The opening 112 is
deeper than conventional contact holes which typically stop at the
surfaces 204a'. One benefit of having deeper openings 112 is that
S/D contacts formed therein will have larger contact areas with the
S/D regions 204a. Other respects of this operation are similar to
those discussed with reference to FIGS. 3A and 3B.
At the operation 16, the method 10 (FIG. 1) forms a first contact
layer 114 in the opening 112. Referring to FIGS. 8A and 8B, the
first contact layer 114 is formed over the surfaces of the opening
112. In particular, it is formed over the surfaces 204a' and 204a''
(FIG. 7B) of the S/D region 204a. The first contact layer 114 has a
conformal profile. In an embodiment, the first contact layer 114
has a thickness ranging from about 2 nm to about 10 nm. The
material and formation of the first contact layer 114 are similar
to those discussed with reference to FIGS. 4A and 4B. In various
embodiments, the material of the first contact layer 114 offers low
or negligible energy barrier for charge carriers flowing into and
out of the transistor channel. The first contact material coupled
with increased contact area to the S/D regions 204a reduces the
contact resistance thereof.
At the operation 18, the method 10 (FIG. 1) forms a second contact
layer 116 in the opening 112 over the first contact layer 114.
Referring to FIGS. 9A and 9B, an S/D contact 118 is formed in each
of the openings 112, conductively connecting to the respective S/D
regions 204a. The S/D contact 118 includes the first contact layer
114 and the second contact layer 116. Other respects of the contact
118, such as dimensions, are similar to those discussed with
reference to FIGS. 5A and 5B.
Third Embodiment
The third embodiment of the present disclosure is now described
with reference to FIGS. 10A and 10B, wherein the device 300 has
been fabricated according to some embodiments of the method 10.
Discussions applicable to both the devices 100 and 300 are
abbreviated or omitted below for the sake of simplicity.
Referring to FIGS. 10A and 10B, the device 300 includes two
horizontal (in the "x-y" plane) rod-shaped channels 304b. In
embodiments, the number of channels and the shape of the channels
in the device 300 may vary. For example, the channels 304b may be
bar-shaped or have other suitable shapes, and there may be one or
more channels. The device 300 includes a gate 108 that wraps around
the channels 304b. Hence, the device 300 is a horizontal
gate-all-around (HGAA) device. Other respects of the device 300 are
the same as or similar to those of the device 200. For example, the
device 300 also includes diamond-shaped S/D regions 304a formed
over the substrate 102 and the fin 104. The process of forming S/D
contacts for the device 300 is the same as what have been discussed
with respect to the devices 100 and 200. An exemplary process of
forming the device 300 prior to the S/D contact formation can be
found in U.S. Pat. No. 8,815,691 entitled "Method of Fabricating a
Gate All Around Device," the contents of which are hereby
incorporated by reference in their entirety.
Examples of the First, Second, and Third Embodiments
FIGS. 10C-10P show S/D regions of various devices (devices 320,
322, 324, 326, 328, 330, 332, 334, 336, 338, 340, 342, 344, and 346
respectively) constructed according to aspects of the present
disclosure. Each of the devices 320-346 may have a channel region
and a gate stack constructed similar to the devices 100, 200, and
300. For example, each of the devices 320-346 may have a fin-like
channel engaged by a gate stack on three sides of the channel, such
as shown in FIG. 9A; or each of them may have a horizontal channel
wrapped around by a gate stack, such as shown in FIG. 10A.
Alternatively, each of the devices 320-346 may have a channel
region and a gate stack constructed differently from those of the
devices 100, 200, and 300. The devices 100, 200, 300, and 320-346
are non-limiting examples. Further examples may be constructed by
combining, substituting, and/or reconfiguring various features of
these devices. For the purposes of simplicity, only the S/D regions
of the devices 320-346 are shown in the respective figures, which
are described below.
Referring to FIG. 10C, the device 320 includes a substrate 102, two
fins 104, two S/D regions 314a formed over the two fins 104, an
isolation structure 106, an ILD layer 110, a first contact layer
114, and a second contact layer 116. The fins 104 extend above a
top surface of the isolation structure 106. The S/D regions 314a
each have a diamond shape and are disposed over top surfaces of the
fins 104. The first contact layer 114 wraps around all surfaces (or
sides) of the S/D regions 314a. A gap between the S/D regions 314a
has a dimension (along the "y" direction) greater than twice of the
thickness of the first contact layer 114. Further, another gap
between the S/D regions 314 and the ILD layer 110 has a dimension
(along the "y" direction) greater than twice of the thickness of
the first contact layer 114. The device 320 may be formed by an
embodiment of the method 10 (FIG. 1). For example, a device
precursor 320 is received at the operation 12, which includes the
substrate 102, the isolation structure 106, the fins 104, the S/D
regions 314a, and the ILD layer 110. The S/D regions 314a are
buried in the ILD layer 110. Subsequently, the ILD layer 110 is
etched at the operation 14 to expose all surfaces of the S/D
regions 314a. Next, the first contact layer 114 is formed at the
operation 16. The first contact layer 114 wraps around all surfaces
of the S/D regions 134. Thereafter, the second contact layer 116 is
formed over the first contact layer 114. Even though FIG. 10C
illustrates the device 320 having two fins 104, in various
embodiments, the device 320 may include any number of fins 104,
such as one fin, two fins, three fins, and so on. In one example,
the device 320 may include one hundred fins 104.
Referring to FIG. 10D, the device 322 includes a substrate 102, two
fins 104, two S/D regions 314a formed over the two fins 104, an
isolation structure 106, an ILD layer 110, a first contact layer
114, and a second contact layer 116. Top surfaces of the fins 104
and a top surface of the isolation structure 106 are substantially
co-planar. The S/D regions 314a each have a diamond shape and are
disposed over the top surfaces of the fins 104. The first contact
layer 114 fully covers two upwardly facing surfaces of the S/D
regions 314a, but only partially covers two downwardly facing
surfaces of the S/D regions 314a. A gap between the S/D regions
314a has a dimension (along the "y" direction) less than twice of
the thickness of the first contact layer 114. As a result, the
respective portions of the first contact layer 114 (on surfaces of
the two S/D regions 314a) merge in the gap. Further, another gap
between the S/D regions 314 and the ILD layer 110 has a dimension
(along the "y" direction) less than twice of the thickness of the
first contact layer 114. As a result, the respective portions of
the first contact layer 114 (on sidewalls of the ILD layer 110 and
on surfaces of the S/D regions 314a) merge in the gap. The device
322 may be formed by an embodiment of the method 10 (FIG. 1), as
discussed above. Further, in various embodiments, the device 322
may include any number of fins 104, such as one fin, two fins,
three fins, and so on. In one example, the device 322 may include
one hundred fins 104.
Referring to FIG. 10E, the device 324 includes a substrate 102, two
fins 104, two S/D regions 314a formed over the two fins 104, an
isolation structure 106, an ILD layer 110, a first contact layer
114, and a second contact layer 116. Top surfaces of the fins 104
and a top surface of the isolation structure 106 are substantially
co-planar. The S/D regions 314a each have a diamond shape and are
disposed over the top surfaces of the fins 104. Portions of the S/D
regions 314a merge. A space (or gap) 316 is formed below the merged
portion, surrounded by two downwardly facing surfaces 314a' of the
S/D region 314a and the top surface of the isolation structure 106.
The first contact layer 114 fully covers upwardly facing surfaces
of the S/D regions 314a, but only partially covers downwardly
facing surface 314a'' of each of the S/D regions 314a. Further, a
gap between the S/D regions 314a and the ILD layer 110 has a
dimension (along the "y" direction) less than twice of the
thickness of the first contact layer 114. As a result, the
respective portions of the first contact layer 114 (on sidewalls of
the ILD layer 110 and on surfaces of the S/D regions 314a) merge in
the gap. The device 324 may be formed by an embodiment of the
method 10 (FIG. 1), as discussed above. Further, in various
embodiments, the device 324 may include any number of fins 104,
such as one fin, two fins, three fins, and so on. In one example,
the device 324 may include one hundred fins 104.
Referring to FIG. 10F, the device 326 includes a substrate 102, two
fins 104, a S/D region 314a formed over the two fins 104, an
isolation structure 106, an ILD layer 110, a first contact layer
114, and a second contact layer 116. Top surfaces of the fins 104
and a top surface of the isolation structure 106 are substantially
co-planar. The S/D region 314a has a hexagonal shape in the "z-y"
plane with a top surface, a bottom surface, two upwardly facing
surfaces, and two downwardly facing surfaces. The top and bottom
surfaces of the S/D region 314a are substantially parallel to the
"x-y" plane (see FIG. 2A). The bottom surface of the S/D region
314a is disposed over the top surfaces of the fins 104. The first
contact layer 114 fully covers the top surface and the two upwardly
facing surfaces of the S/D region 314a, but only partially covers
the two downwardly facing surfaces of the S/D region 314a. Further,
a gap between the S/D region 314a and the ILD layer 110 has a
dimension (along the "y" direction) less than twice of the
thickness of the first contact layer 114. As a result, the
respective portions of the first contact layer 114 (on sidewalls of
the ILD layer 110 and on surfaces of the S/D region 314a) merge in
the gap. The device 326 may be formed by an embodiment of the
method 10 (FIG. 1), as discussed above. Further, in various
embodiments, the device 326 may include any number of fins 104,
such as one fin, two fins, three fins, and so on. In one example,
the device 326 may include one hundred fins 104.
Referring to FIG. 10G, the device 328 includes a substrate 102, a
fin 104, an S/D region 314a formed over the fin 104, an isolation
structure 106, an ILD layer 110, a first contact layer 114, and a
second contact layer 116. A top surface of the fin 104 and a top
surface of the isolation structure 106 are substantially co-planar.
The S/D region 314a has a hexagonal shape in the "z-y" plane with a
top surface, a bottom surface, two upwardly facing surfaces, and
two downwardly facing surfaces. The top and bottom surfaces of the
S/D region 314a are substantially parallel to the "x-y" plane (see
FIG. 2A). The bottom surface of the S/D region 314a is disposed
over the top surface of the fin 104. The first contact layer 114
fully covers the top surface and the two upwardly facing surfaces
of the S/D region 314a, but only partially covers the two
downwardly facing surfaces of the S/D region 314a. Further, a gap
between the S/D region 314a and the ILD layer 110 has a dimension
(along the "y" direction) less than twice of the thickness of the
first contact layer 114. As a result, the respective portions of
the first contact layer 114 (on sidewalls of the ILD layer 110 and
on surfaces of the S/D region 314a) merge in the gap. The device
328 may be formed by an embodiment of the method 10 (FIG. 1), as
discussed above. Further, in various embodiments, the device 328
may include any number of fins 104, such as one fin, two fins,
three fins, and so on. In one example, the device 328 may include
one hundred fins 104.
Referring to FIG. 10H, the device 330 includes a substrate 102, two
fins 104, two S/D regions 314a formed over the respective fins 104,
an isolation structure 106, an ILD layer 110, a first contact layer
114, and a second contact layer 116. Top surfaces of the fins 104
and a top surface of the isolation structure 106 are substantially
co-planar. The S/D regions 314a each have a substantially hexagonal
shape in the "z-y" plane with two upwardly facing surfaces, two
side surfaces, and two downwardly facing surfaces. The two upwardly
facing surfaces are slanted from the "x-y" plane (see FIG. 2A) and
meet to form a ridge. The two side surfaces are substantially
parallel to the "x-z" plane (see FIG. 2A). The two downwardly
facing surfaces are also slanted from the "x-y" plane. The first
contact layer 114 fully covers the two upwardly facing surfaces of
each S/D region 314a, but only partially covers the two side
surfaces of each S/D region 314a. The device 330 may be formed by
an embodiment of the method 10 (FIG. 1), as discussed above.
Further, in various embodiments, the device 330 may include any
number of fins 104, such as one fin, two fins, three fins, and so
on. In one example, the device 330 may include one hundred fins
104.
Referring to FIG. 10I, the device 332 is similar to the device 330
in many respects. Some differences are noted below. In the device
332, the first contact layer 114 does not cover the two outer side
surfaces 314a' of the S/D region 314a. The first contact layer 114
fully covers the two inner upwardly facing surfaces 314a''', but
full or partially covers the two inner side surfaces 314a'' and the
two outer upwardly facing surfaces 314a''''. The device 332 may be
formed by an embodiment of the method 10 (FIG. 1), as discussed
above. For example, when etching the ILD layer 110 at operation 14,
the etching dimensions are controlled such that the surfaces 314a'
are not exposed by the etching process.
Referring to FIG. 10J, the device 334 is similar to the device 332
in many respects. Some differences are noted below. In the device
334, the fins 104 extend above a top surface of the isolation
structure 106 and the S/D regions 314a are each disposed (e.g., by
an epitaxial growth process) over the respective fins 104 without
recessing the fins 104. As a result, the S/D regions 314a each wrap
around the respective fins 104. The device 334 may be formed by an
embodiment of the method 10 (FIG. 1), as discussed above.
Referring to FIG. 10K, the device 336 is similar to the device 320
(FIG. 10C) in many respects. Some differences are noted below. In
the device 336, two outer downwardly facing surfaces 314a' of the
S/D regions 314a are not covered by the first contact layer 114.
The first contact layer 114 fully covers two inner upwardly facing
surfaces 314a'' and two inner downwardly facing surfaces 314a''',
and partially or fully covers two outer upwardly facing surfaces
314a''''. The device 336 may be formed by an embodiment of the
method 10 (FIG. 1), as discussed above. For example, when etching
the ILD layer 110 at operation 14, the etching dimensions are
controlled such that the surfaces 314a' are not exposed by the
etching process.
Referring to FIG. 10L, the device 338 is similar to the device 322
(FIG. 10D) in many respects. Some differences are noted below. In
the device 338, two outer downwardly facing surfaces 314a' of the
S/D regions 314a are not covered by the first contact layer 114.
The first contact layer 114 fully covers two inner upwardly facing
surfaces 314a'', and fully or partially covers two inner downwardly
facing surfaces 314a''' and two outer upwardly facing surfaces
314a''''.
Referring to FIG. 10M, the device 340 is similar to the device 324
(FIG. 10E) in many respects. Some differences are noted below. In
the device 340, the first contact layer 114 fully covers two inner
upwardly facing surfaces of the S/D regions 314a, and fully or
partially covers two outer upwardly facing surfaces of the S/D
regions 314a. Further, it does not cover the downwardly facing
surfaces 314a' and 314a''.
Referring to FIG. 10N, the device 342 is similar to the device 326
(FIG. 10F) in many respects. Some differences are noted below. In
the device 342, the first contact layer fully covers the top
surface of the S/D region 314a, and fully or partially covers the
two upwardly facing surfaces of the S/D region 314a. The first
contact layer does not cover the two downwardly facing surfaces of
the S/D region 314a.
Referring to FIG. 10O, the device 344 is similar to the device 328
(FIG. 10G) in many respects. Some differences are noted below. In
the device 344, the first contact layer fully covers the top
surface of the S/D region 314a, and fully or partially covers the
two upwardly facing surfaces of the S/D region 314a. The first
contact layer does not cover the two downwardly facing surfaces of
the S/D region 314a.
Referring to FIG. 10P, the device 346 is similar to the device 336
(FIG. 10K) in many respects. Some differences are noted below. In
the device 346, the first contact layer 114 fully covers all
surfaces of the S/D regions 314a. Further, the device 346
optionally includes a barrier metal layer 116a between the second
contact layer 116 and the ILD layer 110 and between the second
contact layer 116 and the first contact layer 114. In an
embodiment, the barrier metal layer 116a includes a metal nitride
(e.g., TaN) for preventing the metal elements of the second contact
layer 116 from migrating to adjacent features. The barrier metal
layer 116a is conductive and has a conformal profile, similar to
the first contact layer 114 of FIG. 10K. The device 346 may be
formed by an embodiment of the method 10 (FIG. 1), as discussed
above. For example, a device precursor 346 is received at operation
12 (FIG. 1) that includes the substrate 102, the fins 104, and the
isolation structure 106. The fins 104 extend above the top surface
of the isolation structure 106. The device 346 further includes the
S/D regions 314a disposed over the respective fins 104. Next, the
first contact layer 114 is formed (the operation 16) to fully cover
the surfaces of the S/D regions 314a. Next, the ILD layer 110 is
deposited over the device 346 and covers the first contact layer
114, the S/D regions 314a, and the fins 104. Next, the ILD layer
110 is etched (the operation 14) to form an opening which exposes
portions of the first contact layer 114 except the portions on the
two outer downwardly facing surfaces 314a' of the S/D regions 314a.
Next, the second contact layer 116 is formed in the opening (the
operation 18). In the present embodiment, the operation 18 includes
forming the barrier metal layer 116a (e.g., using CVD or PVD
techniques) before the formation of the second contact layer
116.
In various embodiments, each of the devices 322, 324, 326, 328,
330, 332, 334, 336, 338, 340, 342, and 344 may be formed to have
the first contact layer 114 fully wrapping the S/D regions 314a
before the respective ILD layer 110 is formed, such as discussed
with reference to FIG. 10P.
Fourth Embodiment
The fourth embodiment of the present disclosure is now described
with reference to FIGS. 11A and 11B, wherein the device 400 has
been fabricated according to some embodiments of the method 10.
Discussions applicable to both the devices 100 and 400 are
abbreviated or omitted below for the sake of simplicity.
Referring to FIGS. 11A and 11B, the device 400 includes two
horizontal (in the "x-y" plane) rod-shaped active regions 404.
Source and drain regions 404a and channel 404b are formed in the
active regions 404 and have the same rod shape. In embodiments, the
number and shapes of the active regions 404 may vary. For example,
the active regions 404 may have a bar shape or other suitable
shapes, and there may be one or more of such active regions in the
device 400. Similar to the device 300, the device 400 is also a
HGAA device as its gate 108 wraps around the channels 404b. One
difference between the devices 300 and 400 lies in the
configuration of their S/D regions. The S/D regions 404a are
isolated from the substrate 102 and the fin 104 at least within the
contact holes. Therefore, the first contact layer 114 wraps around
each of the S/D regions 404a, providing the maximum contact area.
As shown in FIGS. 11A and 11B, a portion 116A of the second contact
layer 116 fills the space between the S/D regions 404a after the
first contact layer 114 have been formed around thereof. In another
embodiment where a vertical distance between the two S/D regions
404a along the z direction is not greater than two times of the
thickness of the first contact layer 114, the first contact layer
114 around each of the S/D regions 404a physically contact each
other. The process of forming the S/D contacts for the device 400
is the same as what have been discussed with respect to the devices
100. An exemplary process of forming the device 400 prior to the
S/D contact formation can be found in U.S. Pat. No. 8,815,691
entitled "Method of Fabricating a Gate All Around Device," the
contents of which are hereby incorporated by reference in their
entirety.
Fifth Embodiment
The fifth embodiment of the present disclosure is now described
with reference to FIGS. 12-18. FIG. 12 shows a flow chart of a
method 50 of forming a semiconductor device, particularly a
semiconductor device having a vertical multi-gate structure,
according to various aspects of the present disclosure. The method
50 is merely an example, and is not intended to limit the present
disclosure beyond what is explicitly recited in the claims.
Additional operations can be provided before, during, and after
each of the method 50, and some operations described can be
replaced, eliminated, or moved around for additional embodiments of
the method.
At operation 52, the method 50 (FIG. 12) receives a vertical
multi-gate device prior to the S/D contact formation. An exemplary
vertical multi-gate device, the device 500, is shown in FIGS. 13A
and 13B. FIG. 13A is a schematic perspective view of the device 500
and FIG. 13B is a top view of the device 500 (with the ILD layer
110 removed). The device 500 includes a substrate 102, a first S/D
region (or feature) 104a as a mesa on the substrate 102, and an
isolation structure 106 over the substrate 102 and surrounding the
first S/D region 104a. The device 500 further includes two
rod-shaped mesas over the first S/D region 104a and extending
upwardly along the "z" direction. The middle portions of the two
rod-shaped mesas provide two transistor channels 104b. The top
portions of the two rod-shaped mesas provide two S/D regions 104c.
The first S/D region 104a, the channel 104b, and the second S/D
region 104c are arranged vertically over the substrate. A gate 108
wraps around the transistor channels 104b. Therefore, the device
500 is a vertical gate-all-round (VGAA) device. The device 500
further includes the ILD layer 110 over the substrate 102 and the
isolation structure 106, filling in the spaces between the various
structures. In embodiments, the ILD layer 110 may include one or
more dielectric layers. The material and composition of the various
elements 102, 104a-c, 106, 108, and 110 are similar to those of the
device 100. Exemplary processes of forming the device 500 prior to
the S/D contact formation can be found in U.S. Pat. No. 8,742,492
entitled "Device with a Vertical Gate Structure" and U.S. Pat. No.
8,754,470 entitled "Vertical Tunneling Field-Effect Transistor Cell
and Fabricating the Same," the contents of which are hereby
incorporated by reference in their entirety.
Another exemplary vertical multi-gate device, the device 600, is
shown in FIGS. 14A and 14B. FIG. 14A is a schematic perspective
view of the device 600 and FIG. 14B is a top view of the device 600
(with the ILD layer 110 removed). Many respects of the device 600
are similar to those of the device 500. One difference between the
two devices lies in the shape of the mesa over the first S/D region
104a. The device 600 has a bar-shaped vertical mesa where the
channel 104b and the second S/D region 104c are included or formed
therein. The device 600 is also a VGAA device. The devices 500 and
600 may be considered two variants of the same general type of
devices, and will be discussed collectively below. In particular,
FIGS. 15-18 show cross-sectional views of the devices 500/600 along
the "C-C" line of FIG. 13A for the device 500 and along the "D-D"
line of FIG. 14A for the device 600. FIG. 15 illustrates the
devices 500/600 prior to the S/D contact formation.
At operation 54, the method 50 (FIG. 12) etches the ILD layer 110
and the isolation structure 106 to form an opening 112. Referring
to FIG. 16, the opening 112 exposes a portion of the top surface
104a' and a portion of the sidewall 104a'' of the first S/D region
104a. Since the isolation structure 106 initially surrounds the
first S/D region 104a, it is partially removed in the etching
process to expose the surface 104a''. The opening 112 is deeper
than conventional S/D contact holes which typically stop at the top
surface 104a'. Therefore, the opening 112 offers more contact areas
to the first S/D region 104a than the conventional S/D contact
holes. In some embodiments, the opening 112 may expose more than
two surfaces of the first S/D region 104, for example, a top
surface and two sidewall surfaces, to further increase the contact
area. The etching processes may include a suitable wet etch, dry
(plasma) etch, and/or other processes. In embodiments, the devices
500/600 include a contact etch stop (CES) layer over the first S/D
region 104a and underneath the ILD layer 110. To further this
embodiment, the partial removal of the CES layer can be performed
in a manner similar to that of the method 10 with reference to FIG.
3B.
At operation 56, the method 50 (FIG. 12) forms a first contact
layer 114 in the opening 112. Referring to FIG. 17, the first
contact layer 114 is formed over the surfaces of the opening 112.
In particular, it is formed over the two surfaces 104a' and 104a''
(FIG. 16) of the first S/D region 104a. The first contact layer 114
has a conformal profile. In an embodiment, the first contact layer
114 has a thickness ranging from about 2 nm to about 10 nm. The
material and formation of the first contact layer 114 are similar
to those discussed with reference to FIGS. 4A and 4B. In various
embodiments, the material of the first contact layer 114 offers low
or negligible energy barrier for charge carriers flowing into and
out of the transistor channel. The first contact material coupled
with increased contact areas to the first S/D region 104a reduces
the S/D contact resistance thereof.
At operation 58, the method 50 (FIG. 12) forms a second contact
layer 116 in the opening 112 over the first contact layer 114.
Referring to FIG. 18, an S/D contact 118s is formed in the opening
112, conductively connecting to the first S/D region 104a. The S/D
contact 118s includes the first contact layer 114 and the second
contact layer 116. Other respects of the contact 118s are similar
to those discussed with reference to FIGS. 5A and 5B. In the
present embodiment, the S/D region 104a is a source region of the
device 500/600 and the S/D contact 118s is a source contact.
At operation 60, the method 50 (FIG. 12) performs further steps to
complete the fabrication of the devices 500/600. For example,
operation 50 may form another S/D contact 118d electrically
connecting the second S/D region 104c, as shown in FIG. 19.
Referring to FIG. 19, the S/D contact 118d also includes a first
contact layer 114 and a second contact layer 116, wherein the first
contact layer 114 wraps around three sides of the S/D region 104c.
In an embodiment, the S/D contact 118d is formed by etching the ILD
layer 110 to form an opening that exposes the three sides of the
S/D region 104c (similar to the operation 54), forming the first
contact layer 114 in the opening (the operation 56), and forming
the second contact layer 116 over the first contact layer 114 (the
operation 58). In an embodiment, the S/D contacts 118s and 118d are
formed by the same process that includes the etching of the ILD
layer 110 (the operation 56), the forming of the first contact
layer 114 (the operation 56), and the forming of the second contact
layer 116 (the operation 58). In the present embodiment, the S/D
region 104c is a drain region of the device 500/600 and the S/D
contact 118d is a drain contact.
The method 50 (FIG. 12) may perform further steps to complete the
fabrication of the devices 500/600. For example, it may form a gate
contact electrically connecting the gate 108, and form metal
interconnects connecting the multi-gate FET to other portions of
the device 100 to form a complete IC.
FIG. 20 shows an embodiment of the device 700, constructed
according to various aspects of the present disclosure. Some
differences between the device 700 and the device 500/600 (FIG. 18)
are noted. One difference is that the first contact layer 114 is
formed over the entire top surface of the source region 104a not
covered by the vertical mesa. Another difference is that the source
contact 118s in the device 700 optionally includes a barrier metal
layer 116a between the second contact layer 116 and the layers
surrounding the second contact layer 116. Notably, the source
contact 118s contacts at least a portion of the top surface and a
portion of the sidewall surface of the source region 104a, reducing
the source contact resistance. The barrier metal layer 116a is
conductive and has a conformal profile, similar to the first
contact layer 114 of FIG. 18. In an embodiment, the barrier metal
layer 116a includes a metal nitride (e.g., TaN).
The contact layers 116a and 116 of the device 700 may be formed
with an embodiment of the method 50 (FIG. 12), as discussed above,
wherein the barrier metal layer 116a is deposited (e.g., by a CVD
or PVD process) in the opening 112 (FIG. 16) followed by the
deposition of the second contact layer 116 (FIG. 18). The formation
of the first contact layer 114 is briefly discussed below. In an
embodiment, first, a hard mask 120 and a vertical mesa (104b-c) are
formed over the source region 104a (FIG. 21) using various
deposition and etching processes. Next, a spacer feature 122 is
formed around the vertical mesa (FIG. 22). The spacer feature 122
may be formed by CVD of silicon nitride followed by reactive ion
etching, in one example. Next, the first contact layer 114 is
formed over the source region 104a (FIG. 23) using one of the
techniques discussed above. Next, the spacer feature 122 is removed
(FIG. 24), and the ILD layer 110 and the gate 108 are formed (FIG.
25). Subsequently, an embodiment of the method 50 (FIG. 12) is used
to form the barrier metal layer 116a and the second contact layer
116 as shown in FIG. 20, and may further form a drain contact 118d
as shown in FIG. 19.
Although not intended to be limiting, one or more embodiments of
the present disclosure provide many benefits to a semiconductor
device and the formation thereof. For example, source/drain (S/D)
contact holes etched according to embodiments of the present
disclosure provide larger contact areas to S/D regions of a
transistor than conventional S/D contact holes. Contact holes of
the present disclosure expose multiple surfaces of the S/D regions,
such as a top surface, one or more sidewall surfaces, and/or
surfaces all-around. The larger contact areas contribute to lower
S/D contact resistance. Furthermore, S/D contacts formed according
to embodiments of the present disclosure include two layers of
contact materials. In particular, the first contact layer is
conformal and is in direct contact with the semiconductor material
of the respective S/D region. The material(s) of the first contact
layer offers low or negligible energy barrier for charge carriers
to flow into or out of the transistor channel. The contact material
coupled with the large contact area provides ultra-low contact
resistivity. In experiments, contact resistivity in the range of
1.times.e.sup.-10 to 1.times.e.sup.-8 ohmcm.sup.2 has been
achieved.
In one exemplary aspect, the present disclosure is directed to a
semiconductor device. The semiconductor device includes a
substrate, first and second source/drain (S/D) regions, a channel
between the first and second S/D regions, a gate engaging the
channel, and a contact feature connecting to the first S/D region.
The contact feature includes a first contact layer and a second
contact layer over the first contact layer. The first contact layer
has a conformal cross-sectional profile and either is in contact
with the first S/D region on at least two sides of the first S/D
region or wraps around the first S/D region.
In another exemplary aspect, the present disclosure is directed to
a method of forming a contact in a vertical gate-all-around (VGAA)
device. The method includes receiving a VGAA device having a
substrate, a first source/drain (S/D) region over the substrate, an
isolation structure over the substrate and surrounding the first
S/D region, a channel over the first S/D region, a second S/D
region over the channel, a gate wrapping around the channel, and a
dielectric layer over the isolation structure and the first S/D
region. The method further includes etching the dielectric layer
and the isolation structure to form an opening, wherein the opening
exposes at least two sides of the first S/D region. The method
further includes forming a first contact layer in the opening,
wherein the first contact layer has a conformal cross-sectional
profile and is in contact with the first S/D region. The method
further includes forming a second contact layer in the opening over
the first contact layer.
In another exemplary aspect, the present disclosure is directed to
a method of forming a contact in a multi-gate semiconductor device.
The method includes receiving a multi-gate semiconductor device
having a substrate, first and second source/drain (S/D) regions, a
channel between the first and second S/D regions, a gate engaging
the channel, and a dielectric layer over the first S/D region. The
method further includes etching the dielectric layer to form an
opening, wherein the opening exposes at least two sides of the
first S/D region or wraps around the first S/D region. The method
further includes forming a first contact layer in the opening,
wherein the first contact layer has a conformal cross-sectional
profile and is in contact with the first S/D region. The method
further includes forming a second contact layer in the opening over
the first contact layer.
The foregoing outlines features of several embodiments so that
those of ordinary skill in the art may better understand the
aspects of the present disclosure. Those of ordinary skill in the
art should appreciate that they may readily use the present
disclosure as a basis for designing or modifying other processes
and structures for carrying out the same purposes and/or achieving
the same advantages of the embodiments introduced herein. Those of
ordinary skill in the art should also realize that such equivalent
constructions do not depart from the spirit and scope of the
present disclosure, and that they may make various changes,
substitutions, and alterations herein without departing from the
spirit and scope of the present disclosure.
* * * * *